Centrifugal device



May 5, 1942- w. scHAELcHLlN CENTRIFUGAL DEVICE INVENToR Waiter .Sc/zaeZa/zZi/z.

Filed March 2l, 1959 ATTORNEY Patented May 1942l cENTmUGAL DEVICE Walter Schaelchlin, Wilkinsburg, Pa., assignor to Westinghouse Electric & Manufacturing Company, East Pittsburgh, Pa., a corporation of Pennsylvania Application March 21, 1939, Serial No'. 263,220

1 Claim.

My invention relates to centrifugal devices, and it has particular relation to the stationary element, or the electrical contact-mechanism, of a centrifugal switch such as is utilized on a relatively small, ventilated, self-starting, Single-phase capacitor-motor.

Centrifugal switches ofthe class referred to have requirements which, in some senses, are rather exacting, but which, in other senses, are not so exacting. Since quantity-production methods are applied to the manufacture of such switches, the matter of cost is of paramount consideration, attention beingpaid to even very small fractions of a cent. In many instances, as

in refrigerator motors and in many other smallmotor applications, the matter of extreme silence of operation is also of paramount importance.

A peculiar characteristic of a capacitor motor,v which is a type of motor finding more and more use in small, single-phase motor-applications, is that the centrifugal switchl cannot be permitted to reclose its contacts, when the motor is decelerating, until the motor has decelerated to a rather low speed, as otherwise the motor is likely to self -excite itself, as a result of its residual magnetism and the capacitance which is in series with the capacitor-winding, causing the motor to rapidly stop with an objectionable growling noise.

Another requirement of centrifugal switches= of the type under consideration is that the same basic parts, for economy in the manufacturing operation, will have to be utilizable over a wide range of speeds, as between 600 and 3600 revolutions per minute, by the simple expedient of changing weights and springs.

An example of such small items 0f expense is found in the contact points, which have heretopoor contact-materials.

fore been silver-to-silver contacts, each silverr contact-tip costing in the neighborhood of a half of a cent, and involving a labor-charge of another half of a cent to weld it to the part which carries it. Silver-to-silver contacts have been utilized because this form of contact is the generally accepted form of contact which skilled workers of the art commonly utilize in order to provide good contacts which will stand up in service, with 'a relatively low contact-resistance-drop. As is well-known, silver, and other metals, particularly metals which are basically silver, have the property of maintaining a good conducting surface, without forming a poorly conducting oxide-coating under the operating-conditions of the mechamsm. Such silver-to-silver contacts are'objectionably costly, however, and are also subject to some danger of becoming welded together under and durability are required.

severe arcing conditions such as sometimes obtain when the current through the capacitor-winding is interrupted.

On theother hand, contact-tips of most other available materials are unsuitable, for one reason or another. i Brass and bronze arenotoriously Copper is suitable in other places where it is possible to obtain a suflicient wiping-action to remove the nearlyI nonconducting oxide-film which forms thereon. For small, capacitormotorsl operating on ordinary commercial circuits, such as the 11G-volt lighting circuit, there is only a voltage of 100. to 150 volts available across the contact-tips of the switching mechanism, and this voltage is insufflcient Ito break down two copper-oxide lms, at least with the rapidity required in the rapid startingof motors. Moreover, the' copper-oxide films, even when broken down, have a certain amount' of resistance, resulting in relatively high resistance in the switching contact, a feature which is commonly avoided in applications where long life The result of the foregoing and other considerations is that silver-to-silver contacts have been utilized in the centrifugal switches of capacitor motors, notwithstanding the fact that each small iteml of expense becomes enormously magnified in the large mass-production methods which are utilized inthe manufacture-of these mechanisms.

According to one aspect of my present invention, I have discovered that I can obtain improved results, eliminating the danger of the contacts becoming welded to each other, and I can saveI something like onecent per motor, by utilizing a relatively inexpensive material such as copper or a copper-base metal for one of the contact surfaces, and a silver tip for the other contact surface. It is true that the copper forms a highly insulating oxide coating on itself, but this coating is practically instantaneously broken down at the operating voltages of the order of volts more or less; and it is also true that this copper-oxide lm, even when broken down, results in a contact of fairly high resistance, such as would produce serious' overheating and burning if it were required to carry the rated current for any considerable length of time. I have found, however, that the starting-time of small capacitor-motors is so very small, ranging from l/2 of a second to an extreme maximum of 5 seconds, that there is insufficient time for the Contact to become dangerously overheated before the contact is opened by the operation of the centrifugal mechanism. I have further found that the resistance throughout all of the time that the motor is running, with the exception of the very brief s tarting-period, the centrifugal switch-contacts are open, and the rotation of the motor is causing air-currents to flow over the open contact-points. Most motors of this type are' partially enclosed, with air drawn into the frame at the same end as the centrifugal switch, and blown out by a blower which is necessarily placed at the other v end of the motor, for lack of sufllcient room for both the blower and the centrifugal switch at the same end of the motor, without making the motor-frame larger which is not to be tolerated.

Experience has shown that the air-inlet end of the motor-frame becomes coated with grease and dust on the inside of the frame and on all of the exposed parts therein, whereas the other end of the motor remains cleaner because of the removal of the aforesaid grease and dust from the air. In spite of these conditions, the common forms of centrifugal switch-mechanisms which have heretofore been utilized have had open contacts which were exposed to all of the grease and dust, and which were designed to be operative, even under these adverse conditions.

It is an object of my invention to avoid the difliculties just mentioned by the provision of a dead-air pocket in which the contacting parts are placed, so that grease and dust is not 'carried to the make-and-break surfaces of the contact members.

With the foregoing and other objects in view, my invention relates to the parts, structures and combinations hereinafter described and claimed, and illustrated in the accompanying drawing,

wherein:

Figure 1 is a longitudinal cross-sectional view through'a capacitor-motor embodying my invention, v

Fig. 2 is a diagrammatic view illustrating the electric circuit connections of the motor,

Fig. 3 is an end elevational view of an electrical contact-mechanism constituting the station` ary part of a centrifugal switch in accordance with my invention, the section plane being indicated by the line III- III in Fig. 1,

Fig. 4 is a vertical cross sectional view of the switch-element or contact-mechanism shown in Fig. 3, the section plane being indicated by the line IV-IV in Fig. 3, and

Fig. 5 is a side elevation of the spring .element I of the contact-mechanism.

Fig. 1 shows a typical single-phase capacitormotor embodying my invention. `The motor is ber 8 carrying main and auxiliary windings 9 and I0.

As indicated in Fig. 2, the main andauxiliary windings 9 and I0 are spatially displaced from each other, usually by 90 electrical degrees, and the auxiliary winding I8 is utilized as a capacitor winding in series with a capacitor I2.

The starting and stopping of the motor is usually controlled by a manually-operated startingswitch I3.

Referring again to Fig. 1, it will be seen that a centrifugal switch I4 is disposed within the motor frame, surrounding the motor-shaft 6, at the end of the motor adjacent to the air-inlet opening 3. The stationary part of the centrifugal switch I4 is an electrical contact-mechanism |5- essentially comprising a flat housing I6 which is stationarily mounted within the motor-frame 2 in a position surrounding the motor-shaft B out of contact therewith and at approximately right angles thereto, said stationary llousing carrying a sheet-metal spring-member I8 which also surrounds the shaft without touching the same. The spring member I8 is secured, at its upper end I9, to the supporting housing I6, and at its lower end it carries a contact-tip 2| on the surface facing the supporting housing I6. The resilience of the spring member I8 is such-as to normally hold the contact-tip 2| away from the back of the housing I6, an'd the housing is provided, at

this point, with a stationary contact member 22.

As indicated inv Fig.v 2, the electrical contactmembers 2| and 22 of the centrifugal switch I4 are connected in seriesin the circuit of the capacitor winding I0 and the capacitor I2.

The rotor member ofthe centrifugal switch I4 is in the centrifugal' device proper, which is designated by the numeral 24. Essentially, this rotor member of the centrifugal device lcomprises a -at guide-member 26 which is fixed to the motor-shaft 6 at approximately right angles thereto, supporting the inwardly Iand outwardly moving weight-members 21 which are linked, through finger-members 28, to a slider-member 29 which is slidably mounted on the motor-shaft 6. The finger-members 28 are normally drawn together, toward the shaft, by springs 3|, as illustrated, in the stand-still position of the parts which is shown in Fig. 1. In this position of the parts, the slider-member 29 is pushed away from the guide-member 26, so thatl it engages the contact spring-member I8 of the contact-member I5,

" resulting in the closure of the electrical contact 2|- 22, so that the motor is in a condition ready to be started.

The contact-mechanism I5, which is the socalled stationary part of the centrifugal switch I4, constitutes the special subject of my present invention. One ofthe novel features consists in the provision of a housing or dead-air space 33 for enclosing the contact make-and-break members 2| and 22. This housing or dead-air space is provided by means of a side wall 34 and a spaced front wall 35, both of which are illusprovided with a frame 2 having an air-inlet opening lat one end and an air-outlet opening 4 at the other end, the circulation of air for ventilating purposes being produced by a blower 5 mounted on the motor-shaft 6 adjacent to -the air- I outlet 4. A rotor-member 1, usually of the squirrel-cage type, is centrally disposed on the motor- (shaft 8, in cooperative relation to a stator-inemtrated as being integral with each other and with the rest of the contact-housing I6, al-

though other designs might obviously be used.

It will be noted, from Fig.- 1, that the contacty mechanism- I5 is placed within the motor frame at a point quite close to the air-inlet 3, as previously pointed out. Heretofore, the contacting portions proper, corresponding to my elements 2| and 22, have been entirely exposed, reliance being placed upon the air-blast action to blow the contacts clean, or else a suflicient contactclosing pressure being utilized to, theoretically at least, force the contacts closed in spite of dirt thereon, By the simple expedient of providing a small inexpensive pocket or dead-air space 33, I have at one stroke overcome one of the serious handicaps which have been at the root of many centrifugal-switch. troubles for quite a' number of years. v

A- second feature of my invention relates to the choice or" the materials of the contact makeand-break members 2| and 22. As previously intimated, the forni of construction which was standard prior to my invention has been to utilize a silver tip on each of the members, so as to provide a silver-to-silver contact which is unquestionably good, particularly in its low con tact-resistance, being subject, however, to some slight difficulty in regard to an occasional weld ing of the silver-to-silver contacts as a result of arcing conditions under heavy-current duty.

In accordance with my invention, as previously explained, I utilize contacting surfaces which are of dissimilar metals, so that the welding tendencies are eiectively avoided. I prefer that one of the contacting metals shall be a metal such as silver or a metal which is basically silver, or

other metal which does not form a poorly conenough metal to stand some pitting or wearingA away, without material harm to the operation. I prefer, therefore, since it is necessary to go to the expense of adding some sort of tip 2| to the movable spring-contact members I8, to make this tip 2| the the silver tip, or its equivalent, and to make the other contact-member 22 out of the less-expensive material such as copper.

' Among the advantages of the silver-to-copper contact, I may mention reducing the cost, which is important in devices where mass-production methods are employed, and securing non-welding properties and a contact-reistauce which,

while somewhat high, is nevertheless quiteunobjectionable because of the out-of-phase relation of the capacitive impedance, and because of the extremely short starting-time which is too short a time for overheated-switch diiiiculties to be developed.

In centrifugal switches for motors of the small ratings. it is quite feasible to let the switchcurrent pass through the switch-spring member` i8, as shown in Fig. 3, wherein one of the switchterminals is secured to the fixed upper end-portion I9 of the spring member IB, as indicated at 31, Whereas the other switch-terminati is secured to the stationary contact-member 22, as indicated at 38. Y

As indicated in Fig. 4, the intermedoate portions of; the spring-member i8, where said spring-member straddles the motor shaft E, are

' preferably bowed outwardly in a hump 39, .as is well known in the art, for the purpose of engaging the centrifugal member proper, or the While I have described my invention in a single preferred form of embodiment, it will be obvious that many changes by way of substitutions, additions or omissions may be made by those skilled in the art without sacrificing all of the essential features of the invention. I desire, therefore, that the appended claim shall be accorded the broadest construction consistent with its language and the prior art.

I claim as my invention:

The combination, with a relatively small, single-phase, approximately i10-voltmotor of a type having an intermittent-duty, controlled circuit which has a highly reactive impedance and which is energized for only a very brief time at intermittent intervals, being deenergized at all other times, of an electrical contact-mechanism' connected and operated so as to eil'ect the aforesaid control over said intermittent-duty, controlled circuit, characterized by said electrical contact-mechanism having cooperating, substantially ineii'ectively wiping, contact-making parts ci' dissimilar materials, one of said contactmaking parts being a metallic member which has a copper base, and the other contact-making part being a metallic member which is WALTER SCHAELCHLIN.

slider member 29 of the centrifugal rotor-device 

